1. Field of the Invention
The present invention relates to a control apparatus of a vehicle and more particularly to a control apparatus of a vehicle which includes a so-called dual-clutch type transmission which has clutches and change-speed gear clusters for two systems. In addition, the invention relates specifically to a control when an engine is stopped.
2. Description of the Related Art
As a vehicle's transmission of the related art, there is known a mechanical automatic transmission or a so-called dual-clutch type transmission which includes clutches and change-speed gear clusters for two systems without using a torque converter.
For example, in the dual-clutch type transmission, odd-numbered change-speed gears such as first, third and fifth gears are coupled to one clutch, while even-numbered change-speed gears such as second, fourth and sixth gears are coupled to the other clutch (refer to JP-A-2006-52832).
Synchronizing mechanisms for selecting respective change-speed gears are provided for each system, and a change-speed gear is determined by the synchronizing mechanism, and by applying and releasing alternately the two clutches, the change of gear is effected.
Specifically, while the one clutch is applied, the synchronizing mechanism is caused to mesh with the next change-speed gear to be attained for preparation in the other system, and when a change of gear is effected, the one clutch is released, whereas the other clutch is applied to effect the change of gear.
In a dual-clutch type transmission like that disclosed JP-A-2006-52832, by keeping both the two clutches in the disengaged state, a drive force cut-off state can be produced in which the transmission of drive force from an internal combustion engine (hereinafter, referred to as an engine) to drive road wheels is cut off.
In this way, there may be a case where so-called normally open clutches which can maintain the disengaged state even when the engine is stopped and a power source becomes off are used on a vehicle on which a transmission is equipped in which the drive force transmission is cut off by the clutches being disengaged.
In the vehicle like this, when an ignition switch is switched off, the vehicle can be stopped with the drive force cut off even though the synchronizing mechanism is left meshing with the change-speed gear. In addition, since the clutches are normally open, there is provided an advantage that when the engine is stopped, no electric load is applied.
In addition, where the dual-clutch type transmission is equipped on a vehicle in which a drive force cut-off position where the transmission of drive force from an internal combustion engine to drive road wheels is cut off (for example, a gear shift position such as neutral (N) or park (P)) and a running position where the drive force from the internal combustion engine is transmitted to the drive road wheels (for example, a gear shift position such as drive (D) or reverse (R)) can be selected by a shift lever, there may occur a case where even when the drive force cut-off position is selected, the synchronizing mechanism is made to operate for meshing in an attempt to attain a predetermined change of gear in order to attain the predetermined change of gear quickly, and in the event that the ignition switch is switched off in such a state, the vehicle can be stopped with the synchronizing mechanism left meshing with the change-speed gear.
However, in such a state that the synchronizing mechanism is left meshing with the change-speed gear, an internal resistance of the transmission is large, and when the vehicle is started in such a state, in particular, in the case of the clutches being wet clutches, even though the clutches are released, the internal resistance of the transmission is transmitted as the load of the engine via oil within the clutches, causing a problem that the starting performance is deteriorated.
In particular, when the vehicle is in an extremely low temperature state, the shearing resistance of oil and mechanical resistance of the gears become large, load exerted on the engine when it is started becomes excessively large, leading to a fear that the engine is not started.